I AM a physicist!
Questions like this will depend greatly on a number of factors!
* how much power can the heater provide? if the heater is small, the cold steel would cool off the room, and it would take a while for the heater to catch back up. A large heater will be able to hold the temperature where you want it.
* what is the shape of the steel? Long thin pieces with lots of area exposed to the air will warm much faster than a large chunk.
* what sort of air flow do you have? if the air is still, then it will effectively act like insulation, and the parts will warm up slowly.
* the particular material will matter too. Steel (especially stainless steel) tends to have a low thermal conductivity, which means the "heat" can't travel quickly or easily thru the material.
Tim F